Whiteflies are very small white insects that look much like tiny moths. They can be found on the undersides of leaves, sucking out sap. Adult whiteflies will fly about in clouds when a heavily infested plant is shaken. Immature whiteflies do the most damage to plants; the nymphs, which look like small white raised ovals, fix themselves to leaf undersides and feed for four weeks.
Aside from the visual identification of whitefly on a plant, symptoms include poor growth and leaves that turn yellow, appear dry and wilted, and/or fall off.
Whitefly can spread quickly from one plant to another, so it is important to isolate infested plants. It's also a good idea to isolate newly acquired plants, or those just brought in from the garden, for a few days to make sure no signs of the pest appear.
To control whitefly indoors, use sticky traps. You can buy these or make your own. To make your own, get some bright yellow poster board and cut it into strips. Coat the strips with something sticky, such as Tanglefoot, Vaseline or mineral oil. Place the traps near infested plants, either by hanging it or mounting it on a stakes. Wipe the traps clean every couple days and apply more sticky substance.
Alternatively, suck the adult whiteflies into a small vacuum cleaner, then put the vacuum bag into a plastic bag and freeze it for 24 hours to kill the sucked-up insects. This works best before the infestation becomes heavy.
Insecticidal soap is also a weapon against whitefly. You can buy a prepared soap and follow the directions on the label, or try making your own by mixing one tablespoon of dish detergent in one quart of water, and spraying it on your infested plants. Do this out of direct sunlight, and test it on one section first to be sure the mixture doesn't burn the foliage.